Q150. Consider genetic medicines:
1. They can correct or compensate for defective genes.
2. Engineered viruses and lipid nanoparticles may deliver them.
3. They always rewrite the entire genome.
Which are correct?
[UPSC CSE (Pre) 2026]
- (a) 1, 2 and 3
- (b) 1 and 2 only
- (c) 1 only
- (d) 2 and 3 only
Answer: (b) 1 and 2 only
Explanation: Genetic medicines address particular genes or their products rather than rewriting all chromosomes. Engineered viral vectors and lipid nanoparticles help deliver therapeutic genetic material into cells. Therefore the first two statements are correct, while the third is an overgeneralisation.
Q149. What is the fundamental hereditary material of most cellular organisms?
[UPSC CSE — Practice]
- (a) DNA
- (b) Glycogen
- (c) Cellulose
- (d) ATP
Answer: (a) DNA
Explanation: DNA stores inherited biological instructions through the sequence of its nitrogenous bases. It is replicated and transmitted during cellular division. RNA is the genetic material in some viruses, but most cellular organisms use DNA as their principal information-bearing molecule.
Q148. Which nucleotide base pairs with adenine in ordinary double-stranded DNA?
[WBCS — Practice]
- (a) Guanine
- (b) Uracil
- (c) Cytosine
- (d) Thymine
Answer: (d) Thymine
Explanation: In standard DNA, adenine pairs with thymine through two hydrogen bonds, while guanine pairs with cytosine through three. Complementary base pairing permits faithful replication and accurate copying of genetic information across generations.
Q147. Which sugar is present in the backbone of DNA?
[MPPSC — Practice]
- (a) Sucrose
- (b) Ribose
- (c) Deoxyribose
- (d) Fructose
Answer: (c) Deoxyribose
Explanation: DNA nucleotides contain the pentose sugar deoxyribose, a phosphate group and a nitrogenous base. RNA instead generally contains ribose. The absence of an oxygen at the second carbon helps distinguish deoxyribose chemically.
Q146. A DNA nucleotide consists of which three components?
[UPPCS — Practice]
- (a) Protein, cholesterol and phosphate
- (b) Sugar, phosphate and nitrogenous base
- (c) Glucose, water and enzyme
- (d) Amino acid, lipid and sugar
Answer: (b) Sugar, phosphate and nitrogenous base
Explanation: A nucleotide contains one pentose sugar, one or more phosphate groups and a nitrogenous base. Joining nucleotides through phosphodiester bonds produces a polynucleotide. The base sequence carries information, while the sugar-phosphate backbone provides structural continuity.
Q145. Regarding the GenomeIndia Project, assess:
1. It forms part of the Human Genome Project.
2. It is funded by India’s Department of Biotechnology.
3. It catalogues genetic diversity in Indian populations.
Which statements are correct?
[UPSC CSE (Pre) 2026]
- (a) 2 and 3 only
- (b) 1 only
- (c) All three
- (d) 1 and 2 only
Answer: (a) 2 and 3 only
Explanation: GenomeIndia is a distinct Indian initiative supported by the Department of Biotechnology. It aims to document genomic variation across Indian populations and support research in health and ancestry. It is not a subdivision of the earlier international Human Genome Project.
Q144. Two strands in the usual DNA double helix run in which orientation?
[RAS / RPSC — Practice]
- (a) Perpendicular
- (b) Parallel 5-prime to 3-prime
- (c) Randomly branched
- (d) Antiparallel
Answer: (d) Antiparallel
Explanation: The complementary DNA strands run in opposite chemical directions, one 5-prime to 3-prime and the other 3-prime to 5-prime. This antiparallel organisation allows regular base pairing and is essential to how DNA polymerases copy the strands.
Q143. Which nitrogenous base is usually found in RNA instead of thymine?
[SSC CGL — Practice]
- (a) Adenine
- (b) Guanine
- (c) Uracil
- (d) Cytosine
Answer: (c) Uracil
Explanation: RNA generally uses uracil where DNA uses thymine. Both molecules also contain adenine, guanine and cytosine. Although this is a useful distinction, several modified bases occur in specialised RNA molecules and certain unusual nucleic acids.
Q142. DNA replication is called semiconservative because each daughter molecule contains:
[SSC CHSL — Practice]
- (a) Only fragments of parental strands
- (b) One original strand and one newly synthesised strand
- (c) Two completely newly synthesised strands
- (d) Three DNA strands
Answer: (b) One original strand and one newly synthesised strand
Explanation: Semiconservative replication preserves one parental template strand in each daughter double helix, paired with one newly synthesised complementary strand. Meselson and Stahl experimentally demonstrated this mechanism using nitrogen isotopes in bacterial DNA.
Q141. Which chemical bond connects successive nucleotides along one DNA strand?
[SSC MTS — Practice]
- (a) Phosphodiester bond
- (b) Peptide bond
- (c) Hydrogen bond
- (d) Disulfide bond
Answer: (a) Phosphodiester bond
Explanation: A phosphodiester linkage connects the 3-prime hydroxyl of one sugar with the 5-prime phosphate of the next nucleotide. Hydrogen bonds join opposite complementary bases, whereas peptide bonds connect amino acids in proteins.